The present invention relates generally to the manufacture of small diameter medical devices. More particularly, the present invention is an apparatus and method for manufacturing small diameter ultrasonic probes capable of vibrating in a transverse mode that can be used in ultrasonic medical devices for tissue ablation.
Ultrasonic probes are devices which use ultrasonic energy to fragment body tissue or debris (see, e.g., U.S. Pat. No. 5,112,300; U.S. Pat. No. 5,180,363; U.S. Pat. No. 4,989,583; U.S. Pat. No. 4,931,047; U.S. Pat. No. 4,922,902; and U.S. Pat. No. 3,805,787) and have been used in many surgical procedures. The ultrasonic energy produced by an ultrasonic probe is in the form of very intense, high frequency sound vibrations that result in powerful chemical and physical reactions in the water molecules within a body tissue or surrounding fluids in proximity to the probe. These reactions ultimately result in a process called xe2x80x9ccavitation,xe2x80x9d which can be thought of as a form of cold (i.e., non-thermal) boiling of the water in the body tissue, such that microscopic bubbles are rapidly created and destroyed in the water creating cavities in their wake. As surrounding water molecules rush in to fill the cavity created by collapsed bubbles, they collide with each other with great force. Cavitation results in shock waves running outward from the collapsed bubbles which can wear away or destroy material such as surrounding tissue or debris in the vicinity of the ultrasonic probe. Medical applications for ultrasonic probes include, for example, treatment of cancer, tissue remodeling, liposuction, tissue biopsy, and removal of vascular occlusions.
A drawback of existing ultrasonic medical probes is that they typically remove tissue slowly in comparison to instruments that excise tissue by mechanical cutting, electrocautery, or cryoexcision methods. Part of the reason for the slow removal of tissue is that most existing ultrasonic devices rely on a longitudinal vibration of the tip of the probe for their tissue-disrupting effects. Because the tip of the probe is vibrated in a direction in line with the longitudinal axis of the probe, a tissue-destroying effect is only generated at the tip of the probe. The concentration of energy at the probe tip results in the generation of heat at the probe tip, which can create tissue necrosis, thereby complicating the surgical procedure and potentially compromising the recovery of the patient.
Complications such as these may be avoided by an ultrasonic device which includes an ultrasonic probe whose vibrations are restricted to occur exclusively in a transverse direction to the probe axis (perpendicular). By eliminating the axial motion of the probe and allowing transverse vibrations only, fragmentation of large areas of tissue spanning the entire length of the probe is possible due to generation of multiple cavitational nodes along the probe length perpendicular to the probe axis. Since substantially larger affected areas within an occluded blood vessel, organ, graft or port can be denuded of the occluding tissue or debris in a short time, actual treatment time using the transverse mode ultrasonic medical device is greatly reduced as compared to methods using probes that primarily utilize longitudinal vibration (along probe axis) for tissue or debris ablation. Another advantage to ultrasonic devices which operate in a transverse mode is their ability to rapidly remove tissue or debris from large areas within cylindrical or tubular surfaces which is not possible by devices that rely on the longitudinal vibrating probe tip for effecting tissue fragmentation.
Ultrasonic probes currently known in the art are generally made by a process of machining to achieve a diameter of approximately 0.020 inches, or greater, at the functional end of the probe. Dies are commonly known in the art and are used in the machining process (see, e.g., U.S. Pat. No. 5,840,151; U.S. Pat. No. 5,325,698; U.S. Pat. No. 5,261,805; and U.S. Pat. No. 6,062,059). Although it is possible to induce transverse vibrations at an ultrasonic probe diameter of 0.020 inches (see, e.g., U.S. Pat. No. 5,803,083; U.S. Pat. No. 5,058,570; U.S. Pat. No. 5,469,853; and U.S. Pat. No. 5,421,338), probe diameters less than 0.020 inches are crucial for the generation of sufficient cavitational energy via transverse vibration needed for the treatment of tissue. Since probes vibrating exclusively in a transverse mode must rely almost entirely on generation of sufficient cavitational energy to cause tissue ablation, the diameter of the distal segment of the probe and the probe tip have to be smaller than conventional prior art probes that are only capable of longitudinal vibration. The manufacturing methods for conventional, longitudinally vibrating ultrasonic probes disclosed in the art typically involve machining techniques to obtain probe diameters typically greater than 0.020 inches. Further reduction in probe diameter by such prior art methods is not attainable since the material making up the probe is highly susceptible to fracture.
Prior art attempts to manufacture ultrasonic probes having a small diameter have been less than successful. U.S. Pat. No. 5,527,273 to Manna et al. discloses a method of machining to achieve a diameter of 0.020 inches, or greater, at the distal end of the device. The Manna et al. process results in a probe having limited flexibility and the probe is not capable of producing significant cavitational energy via transverse vibrations. In addition, Manna et al. discloses manufacturing a small diameter device comprising providing a first section, a second section of different diameter, and a means to connect the first section to the second section. Although the small diameter of the distal end of the Manna et al. device allows for generation of cavitational energy, connecting a first section to a second section presents a high likelihood of fracture and an inefficient method of manufacturing the device. Thus, a need exists in the art for an ultrasonic probe having varying diameters that can be manufactured from a single metal stock.
U.S. Pat. No. 5,993,408 to Zaleski discloses a small diameter needle for cutting tissue at a distal end of the device. The Zaleski device, a thin tip phaco needle, comprises a body having a longitudinal bore for enabling passage of cut tissue therethrough. A distal end of the Zaleski device comprises a tip for cutting tissue and a proximal end for engaging a handpiece. The tip includes chamfer means for enhancing cutting efficiency of the tip. The chamfer means may be comprised of a beveled or stepped cutting edge of the tip, having a wide proximal wall and a thin distal wall, the distal wall having a cross section of about half of a cross section of the wide proximal wall. The Zaleski device is limited in that only tissue in contact with the tip of the needle is treated. Additionally, the Zaleski device is not used to create cavitational energy via transverse vibration along the length of the needle and there is no indication that the Zaleski device could be used to provide such energy. Further, the Zaleski patent does not disclose an apparatus or method of manufacturing the needle. Thus, a need exists in the art for an efficient and reliable method to manufacture small diameter ultrasonic probe.
U.S. Pat. No. 4,870,953 to DonMicheal et al. discloses an elongated, solid, flexible probe attached at one end to an ultrasonic energy source and having a rounded probe tip at a distal end, the probe tip being capable of both longitudinal and transverse motion. The DonMicheal et al. device is limited in that it does not disclose the treatment of tissue along a length of the probe and only discloses tissue treatment at the probe tip. Further, the DonMicheal et al. patent does not disclose an apparatus or method of manufacturing a small diameter medical device. Thus, a need exists in the art for an efficient and reliable method to manufacture small diameter ultrasonic probe.
Accordingly, there is a need in the art for an apparatus and method to manufacture small diameter ultrasonic probes capable of vibration in a transverse mode for incorporation in tissue ablation medical devices.
The present invention is an apparatus and method for manufacturing small diameter ultrasonic probes capable of vibrating in a transverse mode that can be used in ultrasonic tissue ablation. More particularly, the present invention provides an apparatus and method of manufacturing ultrasonic probes having a diameter at the functional end of less than 0.020 inches. The apparatus includes a die, a style puller which is used to engage a functional end of the small diameter medical device, and a die room puller which is used to draw the medical device through the die. The die includes a bell-shaped lead-in on a front side of the die and a bell-shaped lead-in on a back side of the die allowing for reversal of the direction of the draw. Reversing the draw during the drawing process allows for introduction of segments of decreasing diameter from a proximal end of the ultrasonic probe to a distal end of the probe, concluding in a functional end of diameter less than 0.020 inches.
The method of the present invention includes heat treating a large diameter medical device, drawing the large diameter device through a die and reversing the direction of the draw of the medical device through the die in order to provide a medical device having a varying diameter along a length of the method device. The method is repeated until a final diameter is reached. The method of the present invention further includes providing a plurality of dies where a subsequent die has a diameter smaller than the previous die enabling a stepwise reduction in a diameter of the medical device until reaching a final diameter of the medical device.
The present invention is an apparatus and method for manufacturing small diameter ultrasonic probes capable of vibrating in a transverse mode that can be used in ultrasonic medical devices for tissue ablation. The present invention provides an apparatus and method of manufacturing ultrasonic probes having a diameter at the functional end of less than 0.020 inches. Furthermore, the probe functions in a transverse mode along the length of the probe as disclosed in Assignee""s co-pending patent applications Ser. No. 09/618,352 and Ser. No. 09/917,471, the entirety of which are hereby incorporated by reference.
The present invention provides for a method of manufacturing a small diameter ultrasonic probe including a drawing and annealing process from a precursor probe of larger diameter obtained by a conventional machining process. The method of the present invention comprises drawing the large diameter probe obtained by machining through either a single die or a series of dies decreasing stepwise in diameter thereby enabling a stepwise reduction in probe diameter to a final value. The dies used in the drawing process are constructed such that they include lead-ins on both sides of the die. The lead-ins are of a bell-shape and allow reversing the direction of the draw, or a retrograde pull that is capable of reducing the diameter of a metallic material such as a pre-machined probe that is drawn through them. Reversing the draw during the drawing process allows for introduction of segments of decreasing diameter either in a continuous or stepwise manner along the longitudinal axis of the probe from a single metal stock, thereby maintaining its integrity and mechanical strength to preclude fracturing during its operation in the medical device.
In one aspect of the present invention, the die is made from materials including, but not limited to, tungsten, stainless steel, carbide, diamond or similar materials known to those skilled in the art and is capable of reducing the diameter of the medical device sequentially by about 1% to 5% with each subsequent draw. In another aspect of the present invention, an assembly of dies are arranged serially, each die smaller than the one before, such that they provide a sequential reduction in diameter of the medical device being drawn through the assembly.
The method of the present invention for manufacturing a small diameter ultrasonic probe includes providing a medical device which has been previously machined to a diameter greater than or equal to 0.020 inches, providing the aforementioned die or die assembly including a lead-in on both sides of each die, heat treating the medical device through an annealing process and drawing the medical device through one to a plurality of dies resulting in the small diameter ultrasonic probe. The method of manufacturing of the present invention may result in the small diameter ultrasonic probe having abutting sections of decreasing diameters. The small diameter ultrasonic probe is in one aspect drawn manually and in another aspect drawn mechanically through one to a plurality of dies. Additionally, a lubricant including, but not limited to, lithium grease, soaps, oils, other greases or other similar lubricants known to those skilled in the art are used to lubricate the die assembly during the drawing process. In one aspect of the present invention, drawing the ultrasonic probe through the aforementioned die assembly provides a method for manufacturing an ultrasonic probe with a small diameter, and further provides a method to decrease the diameter of the said ultrasonic probe by about 1% to 5% with each subsequent draw. The decreased diameter of the said present invention provides increased flexibility of the probe that enables it to vibrate in a transverse mode.
A distinguishing feature of the present invention is the ability to manufacture probes of extremely small diameter (small diameter probes) compared to previously disclosed devices (large diameter probes) without loss of efficiency or efficacy, since the tissue fragmentation process in not dependent on an area of the probe tip (distal end). Highly flexible probes can therefore be obtained to mimic device shapes that enable facile insertion into highly occluded or extremely small interstices without resulting in breakage of the probe or puncture or damage of the tissue or body cavity while ensuring optimal results.
In another aspect of the present invention, the metallic object is exposed to a change in temperature through an annealing process. The annealing process is performed prior to the metallic object being drawn through a single die or intermittently while the metallic object is drawn through a succession of smaller dies. In yet another aspect of the present invention, the annealing process is performed after drawing the metallic object through a number of dies to minimize, eliminate or nullify the work hardening that will have taken place. After the metallic object is annealed at an elevated temperature and subsequently cooled to room temperature the drawing process is resumed. The change in temperature, which results from the annealing process, controls the amount work hardening and the resulting mechanical properties of the small diameter ultrasonic probe. The need for annealing and the degree of annealing will be evident to those skilled in the art. In a further aspect of the present invention, the tip of the small diameter ultrasonic probe is shaped by the process of forging, swaging, lathing, or any process of shaping metal known to those of skill in the art.